Move NoAssertContext to Core test utilities (#12621)

This will allow it to be used in WPF as well.

src/Common/tests/TestUtilities/GlobalUsings.cs

@@ -1,5 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+global using System.Diagnostics;
 global using System.Diagnostics.CodeAnalysis;
 global using Xunit;

src/Common/tests/TestUtilities/ModuleInitializer.cs

@@ -1,7 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.Diagnostics;
 using System.Runtime.CompilerServices;
 
 namespace System;

src/Common/tests/TestUtilities/NoAssertContext.cs

@@ -1,8 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-#nullable enable
-
 using System.Collections.Concurrent;
 
 namespace System;

src/Common/tests/TestUtilities/ThrowingTraceListener.cs

@@ -1,8 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.Diagnostics;
-
 namespace System;
 
 public sealed class ThrowingTraceListener : TraceListener
@@ -12,8 +10,9 @@ public sealed class ThrowingTraceListener : TraceListener
     public override void Fail(string? message, string? detailMessage)
     {
         throw new InvalidOperationException(
-            (string.IsNullOrEmpty(message) ? "Assertion failed" : message) +
-            (string.IsNullOrEmpty(detailMessage) ? "" : Environment.NewLine + detailMessage));
+            $"{(string.IsNullOrEmpty(message) ? "Assertion failed" : message)}{(string.IsNullOrEmpty(detailMessage)
+                ? ""
+                : $"{Environment.NewLine}{detailMessage}")}");
     }
 
     public override void Write(object? o)

src/System.Windows.Forms.Primitives/tests/TestUtilities/GlobalUsings.cs

@@ -1,7 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-global using System.Diagnostics;
 global using System.Diagnostics.CodeAnalysis;
 global using Windows.Win32;
 global using Windows.Win32.Foundation;